Olfactory receptors are what give you a sense of smell. Humans have about 5 million of these to detect aromas, and cats have a whopping 40 to 85 million of these receptors. Therefore, the sense of smell takes the lead in all the feline senses. The cat’s ability to smell is 14 times more sensitive than that of a human.

Jacobsen’s Organ

Besides having such an advanced sense of smell that is 14 times more sensitive than a human they also have another mechanism that enhances their sense of smell. Felines have a special organ called Jacobsen’s organ (or the vomeronasal organ) that is located inside the nasal cavity and opens into the roof of the mouth, right behind the upper incisors. This amazing organ serves as a secondary olfactory system and detects specific chemicals by utilizing nerves that lead directly to the brain. Unlike olfactory cells in the nose, the odor receptors of Jacobsen’s organ do not respond to just ordinary smells. Jacobsen’s receptors pick up chemical substances that have no odor at all. In other words, they work to detect “undetectable” odors.

Jacobsen’s organ communicates with the part of the brain that deals with mating, and its primary function relates to breeding. By identifying pheromones, Jacobsen’s organ provides male and female cats with the information they need to determine if a member of the opposite sex is available.

It is this amazing sense of smell that helps even a defenseless blind newborn baby guide itself to its mother’s teat to suckle, and it comes to know its own teat to which it will try to return at each feed. The nose and the Jacobsen’s organ work together to give the cat an incredible sense of smell. When you see a cat smell another cat then immediately open its mouth part way it is using its Jacobsen’s organ to pick up on pheromones and other scents undetectable to the ordinary nose.

When we greet other people, we use our eyes to see their facial expressions, we may vocalize by saying hello, and shaking hands or possibly a hug. Cats may not be able to shake hands and give a hug, but they have their own way to check out and greet another cat. They may first sniff the face area and or do a head butt. Or they may rub heads together. At this time, they will release pheromones. This will tell each cat what his new-found friend likes to eat and what sort of mood he is in. By simply smelling a feline companion, a cat can determine whether they are male or female, happy or aggressive, healthy or ill. This initial greeting will give each cat a general idea of what the other cat is like but for more detailed information the cats must get up close and personal. This involves butt sniffing.

Butt Sniffing

When one cats puts his nose to another cat’s butt, it does seem a bit disgusting, and many people do not understand why a cat would do this. The answer is anatomical. Inside the rectum are two small sacs called anal glands, which secrete a noxious smelling substance into the rectum through a pair of tiny openings. The glands are emptied naturally when the rectal sphincter muscles contract during a bowel movement. We do not notice a difference in the smell since we do not put our nose there and because the smell is partly masked by the smell of the feces. Humans do not have the sensitive nose that our cats have. When cats sniff butts as a greeting, they can determine a great deal of information about each other. Is a new feline acquaintance a friend or foe? Is he aggressive? Is she in heat? Is she feeling ill? And because the odor is unique to every cat and serves as a form of feline identification, two cats can quickly determine if they have met before.

The very act of sniffing rear ends can establish dominance and set the tone of the relationship. The dominant cat will usually initiate the sniffing, while the more submissive cat waits his turn. A submissive cat may end the sniffing and retreat. A dominant cat may stop sniffing and hiss to end the introduction. Some cats are shy and like to limit the information they give out, so they will simply sit down and clamp their tails over their rectums, reducing the odor they emit.

Sniffing butts may seem gross to us, but think of it as a healthy, socially acceptable form of feline communication. The upside is that this form of communication is a lot quicker than a lengthy introduction!